Indirect dry cooling plants are typically tower arrangements or formations having multiple towers, utilized to dissipate heat from industrial plants using large machinery, such as steam turbines, or industrial processes. For example, one type of cooling tower used in these plants is a chimney-type natural draft cooling tower which has a thin veil of concrete forming the side wall thereof. The chimney is open at the top and is supported above the ground by a plurality of legs, and the space between the lower edge of the veil and the ground defines the cooling air inlet for the heat exchange tower.
In one design of a cooling tower, hot water from a condenser, is directed to the heat exchange units within the tower via a conduit, and the cooled water is directed back to the condenser via the conduit and a pump. As the name suggests, the condenser condenses and cools the exhaust exiting from a turbine and the cooled liquid is pumped to a boiler.
In one example, traditional dry-type heat exchange batteries have finned tubes mounted vertically in pairs and are erected on the ground and concentric to an opening. The batteries are typically V-shaped, so that the heat exchange surface creates a toothed polygon, the teeth of which are directed toward the inside of the tower.
A unit of traditional batteries of dry-type heat exchangers with finned tubes is placed horizontally or in slightly inclined fashion toward the bottom center of the tower, between the upper end of support columns and the upper end of the vertical batteries. The support columns are typically located in a single circular row near the opening inside the tower. Heat exchangers are mounted in pairs in V-shaped configurations, the peaks of which are directed upwards; each of the two units are connected by means of brackets. Because of the radial arrangement of the batteries situated above the air entry, an open space in the shape of a sector whose arc takes the shape of the periphery of the chimney exists between each pair of batteries. The spaces are typically sealed by plates to force the air to cross the batteries. The annular space between the wall and the extremity of the horizontal batteries is sealed off in analogous manner by plates. The same is done with triangular plates for the open space between the upper end of the vertical bottom and the inner end of the horizontal batteries.
Each exchanger unit usually includes two beds. Each unit can be fed with water to be cooled separately or otherwise by means of the heater boxes in which the ends of the tubes of the heat exchange units are connected. Some beds are directly exposed to the cooling air while other beds receive air already partially heated in passing through the first beds.
If the liquid to be cooled is to be circulated in series in each vertical battery and the horizontal battery to which it is affixed, and the cold air is first to meet the ascending current of hot water, the mounting described herein is carried out.
The hot water is typically brought to the tower via a conduit, and deposited in a circular part forming a hot water collector. The collector is provided with a circulation pump, the collector is arranged at right angles to the vertical batteries. Next to the collector, a second circular collector is usually installed and is connected to the conduit to evacuate the cooled water. The orifice of the lower water box of a bed of batteries is connected to the hot water collector; by means of a pipe, the orifice of the upper water box of a bed of batteries is connected to orifice of the water box which is most inside the tower of the bed of batteries. By means of a pipe, the orifice of the water box most inside the tower of a bed of batteries is connected to the orifice of the upper water box of the bed of batteries. By suppressing the internal partition of water boxes of batteries which are most outside the tower, the beds of each horizontal battery are placed into communication with each other. Orifice of lower water box of a bed is connected to the cold water collector.
Since water boxes of the batteries are common to both beds the water circulates automatically from the hot water entry towards the cold water evacuation piping using the beds successively, as soon as the siphon has been primed by a low output pump of greater manometric height than the circulation pump.
The equipment may also have piping that is small in diameter, connected to the highest point of each battery. The pipes evacuate the gas contained in the batteries at the time of the filling of the batteries and the introduction of the gas at the time of the emptying of the batteries. This gas is either atmospheric air, possibly dried, or an inert gas such as nitrogen and its pressure will generally be greater than atmospheric.
The aforementioned dry towers typically have wind screens, analogous to those provided in so-called wet towers, to control the strong winds prevailing in storms, and to minimize the disturbances in the distribution of the air inside the tower. The wind screens consist of flat, vertical walls which extend from the periphery of the tower to the extremities of the batteries, arranged in this case in a cross to divide the cooling system into quarters.
The horizontal batteries are supported directly by the vertical batteries themselves and by a single circular row of poles braced by beams. The latter may, moreover, be replaced by the chimney lintel itself, or by any type of framework. Two gangplanks typically allow for the passage of those persons responsible for surveillance and maintenance of the system.
With the increase of the output of steam turbines, the heat dissipating capacity of conventional indirect dry cooling plants has been required to increase accordingly. This demand has led to the use of extremely tall cooling deltas, up to 30 meters in cases, when a vertical cooling delta arrangement is applied. The cooling delta typically includes of a pair of heat exchanger bundles arranged in delta (i.e., Δ) form, with an apex angle of approximately 60 degrees. In the aforementioned delta arrangement, the two inclined sides are the two bundles, and the horizontal side is an airflow control louver assembly. The delta assembly is supplied with a self supporting prismatic steelwork.
Other solutions have been proposed to increase heat dissipating capacity, for example, a single-pass heat exchanger. However, it does not provide very good heat transfer capabilities. Another example is the use of a larger tube diameter, however, it has too high a pressure drop of the liquid being cooled as the air side pressure drop increases. For good heat transfer, a cross-counter flow pattern is preferred in the deltas, which can be implemented with two passes on the waterside. However, the water has to flow through a 60 meter length of tubes, which involves a high water side pressure loss.
Accordingly, there is a need and desire to provide an indirect dry cooling tower that has good heat transfer and a low pressure drop.